Motor vehicle gearbox

ABSTRACT

Motor vehicle gearbox of the &#34;power shift&#34; type with two intermediate shafts (3, 4) for alternately transmitting an input torque to an output shaft (5). The intermediate shafts each present a pair of lockable gear wheels (10, 11 and 15, 16, resp.), rotatably mounted on respective shafts and lockable by couplings (12, 13 and 18, 19, resp.). The gear wheels engage with a pair of gear wheels (20, 21) common for both the intermediate shafts, mounted rotatably on the output shaft and drivably coupled together in order to allow torque transmission from the one intermediate shaft (3) to the other intermediate shaft (4) via either one or both of the common gear wheels (20, 21).

FIELD OF THE INVENTION

The present invention relates to a motor vehicle gearbox comprising twointermediate shafts for transmission of an input torque to an outputshaft, whereby a first gear wheel, rotatably mounted on eachintermediate shaft and lockable by means of coupling means on respectiveshafts, is in engagement with a common gear wheel rotatably mounted withrespect to the output shaft and lockable for rotation together with theoutput shaft, said gear wheel being arranged to transmit torque from oneintermediate shaft to the other in the disengaged position.

BACKGROUND OF THE INVENTION

Two main types of gearbox of the above mentioned type are known forexample from U.S. Pat. Nos. 5,150,628 and 5,388,472. Both these gearboxtypes are so-called "power shift" gearboxes in which the torque istransmitted alternately via both the intermediate shafts to the outputshaft, which means that whilst the torque is being transmitted by one ofthe intermediate shafts the next gear is preselected on the otherintermediate shaft, whereby gear changing itself occurs in that thefirst intermediate shaft is disengaged and the other is engaged. Thiscan be achieved either by driving the input shaft of each of theintermediate shafts and alternately engaging the input shafts via a pairof clutches outside the gearbox as shown in the aforementioned U.S. Pat.No. 5,388,472, or by driving both intermediate shafts from a commoninput shaft via friction clutches arranged within the gearbox housing asshown in the aforementioned U.S. Pat. No. 5,150,628.

A characteristic of these known gearboxes is that the torque in a gearstage, namely the lowest gear, is transmitted via both intermediateshafts by means of a common gear wheel. In this way an additionalreduction stage is achieved compared with the torque transmission, viaonly one intermediate shaft at a time, which allows the possibility ofhigher gearing in the lowest gear than can otherwise be obtained.Alternatively, for a given gearing, larger gear wheels can be used thanwith torque transmission via an intermediate shaft. The constructiongives an extra gear stage without the gearbox needing to be complementedwith additional cooperating gear wheels. The result is a very short andcompact gearbox with a large number of gears.

OBJECT OF THE INVENTION

The object of the present invention, starting from the gearbox describedin the introduction, is to achieve a compact gearbox with many gearstages and with larger span, that is to say larger separation betweenthe lowest and highest gears than can practically be obtained with thedescribed known gearboxes.

SUMMARY OF THE INVENTION

This is achieved according to the invention in that at least a secondgear wheel on each intermediate shaft is in engagement with at least asecond common gear wheel which is driveably coupled to the first commongear wheel in order to allow torque transmission from said first gearwheel on said first-mentioned intermediate shaft to said second gearwheel on the second intermediate shaft via both the common gear wheels,and in that the second intermediate shaft is divided into two partsrotatable relative to each other, said parts being able to be coupled toeach other by coupling means for rotation as a unit.

By creating an additional reduction stage in this way with a secondcommon gear wheel which is smaller than the first common gear wheel, anextremely high gearing can be achieved in the lowest gear. Moreover twoadditional gears are obtained which, starting from the seven-geargearbox of the above described known types, give a compact nine-geargearbox with larger span than can be achieved in these.

BRIEF DESCRIPTION OF THE INVENTION

The invention will now be described in more detail with reference to theembodiments shown in the accompanying drawings wherein FIG. 1 and 2 aretwo identical figures of a schematically represented gearbox with thetorque flow depicted on the different gears.

DETAILED DESCRIPTION OF THE INVENTION

In the figures, numerals 1 and 2 denote two concentrically mounted inputshafts, 3 a first intermediate shaft, 4 a second intermediate shaft and5 and output shaft. One of the input shafts drives the firstintermediate shaft 3 via a pair of gear wheels 6 and 7 respectivelyfixed against rotation on respective shafts. The second input shaft 2drives the second intermediate shaft 4 via a pair of gear wheels 8 and 9respectively fixed against rotation on respective shafts. In the shownembodiment it is presumed that both input shafts I and 2 are alternatelyengageable and disengageable respectively by means of friction clutches(not shown in detail), such as shown in U.S. Pat. No. 5,388,472, foralternately driving the intermediate shafts 3, 4.

The first intermediate shaft 3 supports two freely rotatably mountedgear wheels 10 and 11 which are lockable to the intermediate shaft 3 bymeans of each one's clutch sleeve 12 and 13 respectively and of whichgear wheel 11 comprises a second gear wheel. A first, second and thirdgear wheel 14, 15, and 16 are freely rotatably mounted on the secondintermediate shaft 4 which is divided into an input shaft portion 4a andan output shaft portion 4b which are freely rotatably mounted withrespect to each other. A fourth gear wheel 17 is fixedly mounted on theintermediate output shaft portion 4b. The gear wheels 14 and 15 areengageable by means of a clutch sleeve 18 whilst the gear wheel 16,which comprises a third gear wheel is engageable by means of clutchsleeve 19 which also has an engagement position in which both the shaftportions 4a and 4b are locked together to be driven as an unit.

The shafts lie in a V-formation and the gear wheel 14 on theintermediate shaft 4 engages with gear wheel 7 on intermediate shaft 3.The gear wheels 10 and 15 on shafts 3 and 4 respectively engage with afirst common gear wheel 20 which is rotatably mounted on the outputshaft 5 whilst the gear wheels 11 and 16 on the shafts 3 and 4respectively engage with a second common gear wheel 21 with smallerdiameter than gear wheel 20.

The gear wheel 21 is also rotatably mounted on the output shaft 5. Inthe shown embodiment the gear wheels 20, 21 are fixed onto a common hub22 which is lockable to the output shaft in an engagement position ofthe clutch sleeve 23. In another engagement position of the clutchsleeve 23, the input shaft 1 and the output shaft 5 are coupled togetherfor rotation as a unit. An additional gear wheel 24 on the output shaft5 is rotatably mounted on the shaft and lockable to this by means of aclutch sleeve 25. The gear wheel 24 engages with the gear wheel 17 onthe intermediate shaft portion 4b. As an alternative to the shownembodiment, the gear wheel 16 can be fixedly mounted on the intermediateoutput shaft portion 4b and the gear wheel 21 can be rotatably mountedas well as being lockable to the hub 22 by clutch means.

The clutch sleeves 12, 13, 18, 19, 23 and 25 can be included in theclutch arrangements which comprise conventional synchronization devices,but the described gearbox is particularly designed to make use of acentral synchronization arrangement of the type which is shown anddescribed in the introductory portion of the cited publications.

The gearbox which is shown and described has nine gears, whereby thetorque is transmitted to the output shaft 5 alternately between theinput shaft 1 and 2, the intermediate shaft 3 and the intermediate shaftportions 4a, 4b, via the following cooperating gear-pairs, as indicatedby the arrows I-VIII in the figures:

    ______________________________________                                        First      6,7 → 10,20 → 21,16 → 17,24;                  Second     8,9 → 15,20 → 21,16 → 17,24;                  Third      6,7 → 11,21 → 21,16 → 17,24                   Fourth     8,9 → 17,24;                                                Fifth      6,7 → 10,20;                                                Sixth      8,9 → 15,20;                                                Seventh    6,7 → 11,21;                                                Eighth     8,9 → 16,21                                                 Ninth      Direct drive from the input shaft 1 to the                                    output shaft 5 with clutch sleeve 23 in the                                   aforementioned second coupling position                            Reverse    6,7 → 7,14 → 15,20 → 21,11 →           ______________________________________                                                   17,24;                                                         

From the table above it is clear that the common gear wheels 20, 21 areused at the same time with torque transmission in first and second gearsin order to give extra high gearing in these gears by means of theadditional reduction stage which is thus obtained. Additionally it isclear that the clutch sleeve 19 has an engagement position in eight gearwith which the intermediate shaft portions 4a, 4b are coupled togetherat the same time as the gear wheel 16 is locked to the axle portion 4b.This is also true correspondingly for the clutch sleeve 18 which inreverse locks both the gear wheel 14 and the gear wheel 15 to theintermediate shaft portion 4a.

The invention has been described above with reference to a preferredembodiment having nine forward gears. Additional gearing stages can beachieved with more than two common gear wheels according to thedescribed principle.

The invention is of course not limited to a gearbox of the abovedescribed type with two input shafts, but can be used in a gearbox withone single input shaft, for example of the type shown in U.S. Pat. No.5,150,628.

I claim:
 1. In a motor vehicle gearbox, comprising two intermediateshafts for transmission of an input torque to an output shaft, whereby afirst gear wheel, rotatably mounted on each intermediate shaft andlockable by means of coupling means on respective shaft, is inengagement with a common gear wheel rotatably mounted with respect tothe output shaft and lockable for rotation together with the outputshaft, said gear wheel being arranged to transmit torque from oneintermediate shaft to the other in the disengaged position; theimprovement comprising at least one second gear wheel (11, 16) on eachintermediate shaft (3, 4) engagement with at least a second common gearwheel (21) which is drivably coupled to a first common gear wheel (20)in order to allow torque transmission from said first gear wheel (10) onsaid first-mentioned intermediate shaft (3) to said second gear wheel(16) on the second intermediate shaft (4) via both the common gearwheels (20,21), the second intermediate shaft (4) being divided into twoparts (4a, 4b) rotatable relative to each other, said parts beingengageable with each other by means of coupling means (19) for rotationas a unit.
 2. Gearbox according to claim 1, wherein the secondintermediate shaft (4) comprises an input shaft portion (4a) and anoutput shaft portion (4b) which, in the shaft portions' disengagedposition, allows torque transmission from the input shaft portion to theoutput shaft portion via the first and second common gear wheel (20 and21 resp.).
 3. Gearbox according to claim 1, wherein the second commongear wheel (21) has a smaller diameter than the first common gear wheel(20).
 4. Gearbox according to claim 1, wherein the second common gearwheel (21) is arranged--when the first common gear wheel (20) isdisengaged from the output shaft (5)--to transmit torque via firstgear's gearing with a locked first gear wheel (10) on said firstintermediate shaft (3) and locked second gear wheel (16) on the secondintermediate shaft (4).
 5. Gearbox according to claim 1, wherein thesecond common gear wheel (21) is arranged to--when the first common gearwheel (20) is disengaged from the output shaft--to transmit torque viathird gear's gearing with a locked second gear wheel (11, 16) on boththe intermediate shafts (3, 4).
 6. Gearbox according to claim 1, whereinboth the common gear wheels (20, 21) are mounted on a common hub (22)which is rotatably mounted on the upper shaft (5) and lockable to thisby means of coupling means (23).
 7. Gearbox according to claim 1,further comprising coupling means, by means of which an input shaft (1)and the output shaft (5) are engageable for torque transmission directlyfrom the input shaft to the output shaft.